Retroreflective materials are widely used in a variety of situations involving vehicle and pedestrian traffic. Retroreflective materials promote safety by improving the visibility of objects illuminated by vehicle headlights or other sources of light. In one such application, the circumference of both of the spoked wheels or tires of a bicycle are retroreflective. The retroreflected image of two circles separated by a fixed distance is quite recognizable as a bicycle, even if the other portions of the bicycle are not retroreflective. Unless viewed perpendicularly to the wheel, the circles are seen as ellipses, but the image is still recognizable as a bicycle.
Bicycle tires with retroreflective sidewalls are more expensive than conventional tires, and require replacement of existing non-retroreflective tires. Accordingly, products suitable for addition to bicycles with conventional tires have been developed. Objects which may be added to existing bicycles to create a circular image include those taught by U.S. Pat. Nos. 3,834,765 (Trimble) and 4,285,573 (Stone); European Patent Office Publications 0 003 498 (Trimble) and 0 094 700 (Oskam); and German Offenlegungsschrift 27 50 200.
Retroreflective materials generally have confined angularity, i.e., they brightly reflect light only within a narrow range of solid angles around a ray of incoming light. In many applications this is not a serious disadvantage, because the retroreflective material may be designed and placed so that the intended observers are always within the preferred narrow angular range. For example, many retroreflective materials are designed to retroreflect rays which lie very nearly on the line normal to the surface of the material. Traffic signs made with such materials may be placed to retroreflect light to the known positions of vehicles on a roadway. Bicycles, by contrast, may be traveling in a variety of directions when in the field of view of an observer. Thus, the circular image should be visible from all angles, including directly ahead of and behind the bicycle. The shapes of bicycle reflectors have been designed to complement the properties of retroreflective materials and thereby improve the visibility of the reflectors from all angles.
For example, U.S. Pat. No. 3,834,765 (Trimble) teaches an elongated tubular member which is intertwined among the spokes of the wheel. The curved outer surface of the member ensures that light coming from substantially any direction will strike some portion of the reflective surface within the most efficient angular range of the reflective material.